Painting is the process of coating the surface of the object (to be painted) with some suitable solution of metal in order to avoid the corrosion at the surface with the passage of time. Corrosion occurs due to oxidation of metal at surface of object. The coating applied thereby breaks the contact of oxygen with the surface of the metal thus avoids the corrosion. Moreover painting improves the life, look and shining of the object which are the most important factors, which a customer seeks while, searching for quality products in market.
Painting section involves the following section of operations:- 1. Automatic phosphate paint
2. Primer section 3. Paint section 4. Flash-off section 5. Paint baking oven 6. Inspection
A closed roller conveyor is installed all over the paint section. This chain conveyor step wisely passes through all the process stated above. The component to be painted is hanged on the chain conveyor through the hooks which are rotatable.
1. AUTOMATIC PHOSPHATE PLANT: -
After the assembly of propeller shaft, it is send to paint section for paint but the shaft is not clean enough to undergo painting straight away. Some particles of dust and grease are sticked to it which has to be removed properly for obtaining better results after painting. Moreover the surface of the shaft should be adaptor enough to the solution of primer i.e. primer and paint should stick on the surface properly after phosphating.The automatic phosphating plant is further divided on the bases of different processes as following: - i. Pre-degreasing ii. Degreasing iii. Washing iv. Activation v. Phosphating vi. Passivation vii. Washing
i. PRE-DEGREASING: - Degreasing is the process of removal of grease, oil, dust or
other foreign particles from the surface of the components. Degreasing is done by spraying degreasing water on the propeller shaft which is made mixing 25-30 kg of ACLIEN 60 with 1000 it‟s of ordinary water. The temperature during spray should be of range 55-65°C. Now the mixture of degreasing water is checked every time before spray for optimum strength, suitable for spraying. This is done by titration of degreasing water against hydraulic acid(HCL) 10ml of degreasing water is put in a titration flask. 2-3 drops of indicator named as phenolphthalein is put in it which changes the colorless solution of degreasing water to pink. Now hydraulic acid or HCL is put in burette and it is put drop wise in the pink solution of flask. The color of solution changes from pink to colorless. So, initial and final Readings are noted down and subtracted. The above process is repeated 4-5 times. Concurrent reading is the desired one. This reading should be of range 22-25ml. if the reading came by titration is less than 22 then 3.5kg of Adein is added for every 1ml low value in reading in degreasing water solution to make the strength or the same appropriate to remove the grease and dust to optimum level.
ii. DEGREASING: - This is the final process of degreasing in which the steps
involved in pre degreasing are repeated to get of the impurities like grease, oil, dust etc. completely.
iii. WASHING: - Washing of propeller shaft is done there after with ordinary water in
washing zone of automatic phosphating plant. Some quantity of chemical might have stick to propeller shaft which is now removed by washing.
iv. ACTIVATION: - Activation is process to activate the propeller shaft for
phosphating. In this process accelerator known as IETA CELL is used which produces large quantity of foam instantaneously which helps to activate phosphating process.
v. PHOSPHATING: - In this process a mixture of Meta phosphate and de-mineralized
water is sprayed on the propeller shaft at 45-55°C to produce very small pores of micron on the surface of shaft. The grain size layer thus produced on surface facilitates the grip of paint on the same, making the surface aesthetic. Thus phosphating enhance the strength of grip of paint over the surface of shaft giving good paint without any defect at the end.
vi. PASSIVATION: - In this the phosphating process is repeated on the component to
achieve quality surface over the whole component. Thus covering the surfaces left in initial phosphating process.
vii. WASHING: - After phosphating component is washed with de-mineralized water
which is free from any mineral or salt. The purpose of using de-mineralized water is due to the fact that in ordinary water, impurities like salt or minerals can react with surface of metal of shaft and can stick to it and surface can become rustic resulting in non-proper sticking of paint with the surface.
If the customer does not want to undergo automatic phosphating process on his
component then the same is wiped with a sponge dipped in adeobond and de- mineralized water for removing the impurities from the surface of component. Finally the component is air-dried for further operations.
2. PRIMER SECTION: -
Before painting, the component is sprayed with the primer to avoid paint consumption since primer has less cost than paint and it results in more gripping of paint. Primer is applied before painting. Primer solution is made by adding 1000ml of primer with sufficient amount of thinner which settles the viscosity of primer.3. PAINT SECTION: -
A solution of 1000ml of paint with 300ml of thinner is sprayed on primer component. The primer and paint used here are of L.C.I. Company.PAINT CONVEYER
4. FLASH-OFF ZONE: -
This zone is dust free, maintained at room temperature and is attached with exhaust fan or impeller at the top. The purpose of impeller is to evaporate the thinner inside the paint baking oven, as temperature is high and thinner can catch fire. Moreover some suitable gap is maintained between primer section, painting section and flash-off zone. The time the component travels from one section to another thinner evaporates.5. PAINT BAKING OVEN: -
The component is kept in baking oven for 45 minutes which is maintained at 82C from inside. Baking oven is a large steel chamber through which the component is made to enter from one side through conveyer and it gets out after 45 minutes of baking from the same side.PAINT BAKING OVEN
Baking is the most important part of the whole painting process because it imparts many qualities to the component which are very necessary for a component in a long run. Some of them are listed below: -
Baking imparts glossiness or shining to the component, making it good looking. Since the inside of baking oven is dust proof therefore there is no chance of dust
particle sticking on the surface of component. The appearance otherwise might have been dull if the whole procedure would have been done is open air for long time.
Baking takes just around 45 minutes for its completion. Thus it saves lot of time
as compared to ordinary process in which we keep the component straight in sunlight taking lot of time to import the desired qualities to product.
Painting strength on the surface is significantly increased which increases the life
of component and its working under several conditions
The paint moreover gets dried-up after baking more early.
After automatic phosphating and painting the product is finally send to dispatch section, but before that product is finally inspected.
6. FINAL INSPECTION: -
Though the inspection process is performed in various stages of operation, but final inspection of the whole assembly is necessary for the supplier and customer satisfaction at the final dispatch stage. Following points are kept in mind during inspection of propeller shaft:-a) FACE ALIGHMENT: - The faces of the half yoke welded with the propeller shaft
should be in alignment with each other. If found guilty the pieces found rejected and send to re-welding or it sold in scrap.
b) CIRCLIP CHECK: - Circlip is checked which is attached on bearing cup. If not
c) CHECK BALANCING: - The balancing weights attached on the propeller shaft are
hit by the alight hammer for proper fixation of the weights on the shaft.
d) SLEEVE YOKE CHECKING: - Movement of sleeve yoke should be easy with no
jerk. If jerk is observed, roller bearing should be checked and if necessary reinstalled.
e) PAINTING THICKNESS CHECKING: - Painting thickness is checked with micro
test which should be 40 micron. Small variation in thickness is bearable.
f) PAINT CHECK: - Paint should not detach from the surface while rubbing it with
nail. Moreover there should be no corrosion below the paint if found means automatic phosphating is not done properly which can lead to rejection of materials.
g) NO DUST MARK: - There should be no mark of dent on the surface of the shaft if
found the same should be corrected.
In the way various other factors like shining, paint strength, resistance of paint to water and air, and scratch capability etc. are inspected and finally satisfied in every respect, the component is sent to dispatch store for dispatch.